Oriented strand board (“OSB”) has been manufactured since approximately 1978 and typically includes three to four layers of wood flakes or strands which are compressed to create a panel. Wood flakes or strands are removed from whole logs and placed in wet bins. The strands are then dried to an appropriate moisture content and treated with additives, such as a resin and/or a wax. Next, the strands are formed into a mat during which time they are oriented, or aligned, in a selected direction for each layer. To accomplish this, a device known as a “former” drops strands onto a screen from a small height. In some applications, no screen is provided and the former drops strands directly onto a conveyor belt running below a series of formers. Typically, formers are positioned similar to an assembly line to deposit the strands prior to compression.
A typical panel has a first layer, often referred to as a “top surface” layer which has strands aligned in a longitudinal direction, or, along a longitudinal axis of the layer. A second layer, referred to as a “core” layer, is placed underneath the top surface layer. The core layer may be the product of two sub-layers of deposited strands. The strands of the core layer are aligned in a direction non-parallel to the strands of the top surface mat. Typically, the strands are aligned in a direction perpendicular to the strands of the top surface layer. A third layer, referred to as a “bottom surface” layer, is underneath the core layer and has strands which are aligned substantially parallel to the top surface layer. If the longitudinal direction of the layers is considered as a major axis defining a normal line, then, on average, the strands for the top surface layer and the bottom surface layer deviate from the normal line at a positive/negative 15 to 30 degree angle. This measurement is referred to as a “strand angle” for the layer. For example, a strand angle of 20 degrees would refer to a layer having an average deviation of positive/negative 20 degrees from the normal.
Aligned strands of a layer may be considered similar in property to grain in a wood sample. It is generally known that wood is stiffer and stronger in the grain direction. For example, a wood sample may bear a heavier load that is applied in a direction parallel to the grain than a load applied in a direction non-parallel to the grain. In an oriented strand board panel, each successive layer contains strands which are aligned in a different direction. Therefore, OSB panels have no uniform orientation for the strands as demonstrated by grain in a natural wood. As a result, an OSB panel may bear loads applied in a variety of directions.
Although OSB panels exhibit considerable stiffness when bearing loads, it is desirable to produce OSB panels having increased stiffness to, for example, provide less deflection under a load. One possible solution is to align a greater number of strands in the top surface and/or bottom surface substantially parallel to the longitudinal axis of the layers. One proposed method of achieving this goal is to place discs or vanes within formers closer together to force the strands to drop onto a conveyor belt in a more uniform orientation. However, positioning the discs closer would cause a plug to form between the discs or vanes. This would create a slowdown or stoppage in the production of panels. To prevent this, a manufacturer could reduce the flow of strands to formers; however, this is also undesirable because it leads to less productivity. Most importantly, aligning additional strands at an angle substantially parallel to the longitudinal direction of the top surface layer and/or the bottom surface layer results in fewer strands aligned in a non-parallel direction. The end result is significantly decreased strength in the non-parallel direction of the panel.
A need, therefore, exists for an oriented strand board panel having improved strand alignment with respect to a longitudinal axis of a panel wherein properties of the panel are not significantly compromised in a direction non-parallel to the major axis.